This invention relates to thermoplastic interlayer having rough surfaces and more particularly to a particular form of rough surface for optimum deairing in a prelaminate with glass.
Thermoplastic interlayer (sometimes called "sheet" herein), typically of polyvinyl butyral (PVB), is known for use with optically transparent glass in laminated safety glass assemblies used, for example, in vehicle windshields, building windows and the like.
It is further known, (see, for example, U.S. Pat. No. 4,035,549, to Kennar) to roughen the major surfaces of the sheet to facilitate deairing, i.e. evacuating air from an interface between the sheet and a glass layer during preparation of a prelaminate of the sheet with glass. More specifically, minute channels between the smooth surface of the glass and the rough surface of the opposing contiguous sheet form routes for air to escape from between the two members when pressure or vacuum is applied with heat during preparation of the prelaminate. The deaired prelaminate is then subjected to elevated temperature and pressure bonding conditions, usually in a downstream autoclave, to form the finished safety glass assembly.
Inadequate deairing results in visual defects in the finished safety glass assembly in the form of undesirable bubbles or local unlaminated regions. Deair completeness is conveniently measured by light transmission through the prelaminate before final laminating in the autoclave. The greater such transmission, the greater the quality of deairing provided by a particular profile of rough surface.
Optimum deairing continues as a need in the laminated safety glass art.
A surface profile to optimize deairing is disclosed in commonly assigned, copending U.S. application Ser. No. 08/106,742, filed Aug. 16, 1993, titled Rough-Surfaced Interlayer. However, as therein noted in Example C1, to avoid the presence in the interlayer of an undesirable moire appearance, the roughness surface profile is different on each side of the sheet. Moire patterns typically visually resemble a kind of plaid or wood grain appearance usually as a result of superimposed regular patterns on each side of the interlayer. It would be desirable to avoid moire without the complexity of developing radically different surfaces on each side of the interlayer.